Lined pipeline vent

ABSTRACT

The present invention relates to apparatus for use in venting pipelines that have a plastic lining such as these used for transporting hydrocarbon fluids. A pipeline assembly comprises a pipeline ( 2 ), a corrosion resistance liner ( 3 ), and a micro-annulus ( 4 ) located between said pipeline and liner. The pipeline assembly also comprises a venting means ( 5 ) adapted for fitment in or through the corrosion resistance liner ( 3 ), wherein the venting means ( 5 ) allows gas to flow from the micro-annulus into the center of the pipeline assembly but not in the opposing direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national phase of International (PCT) PatentApplication Ser. No. PCT/GB01/04546, filed Oct. 12, 2001, publishedunder PCT Article 21(2) in English, which claims priority to and thebenefit of British Patent Application No. 0025301.3, filed Oct. 14,2000, the disclosures of which are incorporated herein by reference.

The present invention relates to apparatus for use in venting pipelinesthat have plastic lining. In particular the present invent ion relatesespecially but not exclusively to plastic lined pipelines used fortransporting hydrocarbon fluids.

Pipelines employed in the oil production industry are commonly used tocarry aggressive and corrosive hydrocarbon fluids. This is problematicas pipelines of this type are often run at considerable depths and it isboth costly and time consuming to repair and replace any damage whichmay occur as a result of corrosion of the pipeline. Unfortunately,corrosion resistant materials are very expensive and hence undesirablefor manufacturing pipeline, which may be hundreds of meters in length.

There are therefore considerable cost benefits in using Carbon Steelpipelines lined with cheap corrosion resistant liner. Indeed a number ofplastics material liners have previously been proposed and are commonlyused in process plant pipework. Although effective for this purpose, thematerials used in process plant pipework systems are not suited for usein petrochemical pipelines as they are typically supplied in shortlengths that are flanged rather than welded and operate at near ambienttemperatures and low pressures. They are therefore not suitable forhydrocarbon pipelines which are subject to hostile chemical and pressureconditions.

In applications where non-hydrocarbon pipelines, which carry fluids withno gaseous content, are lined by a plastic liner, it is typical to weldtogether significant lengths of the steel pipeline and then to pull acontinuous plastics material pipe into the steel pipe to form an innerlining. This is achieved by swaging or squeezing the plastic materialbetween rollers to make it temporarily smaller such that it fits within;the pipeline in a loose fit. When the plastic material relaxes, or isexpanded, it achieves a close fit with the steel pipeline. However thereis no physical bond between the pipeline and the plastic liner and as aconsequence a small micro-annulus exists between the two.

The plastic materials used are typically slightly permeable. As aresult, small gas molecules permeate out of the fluid stream in thepipeline and pressurise the micro-annulus between the steel pipeline andinner plastic liner. During normal operational practices fluid pressurein the pipeline fluctuates over time. When this fluctuation is apressure drop the gas trapped in the annulus expands and collapses theliner, which can not be re-flated thereafter without damage.

This invention relates to improvements to our earlier British PatentApplication Number 9817223.2 which teaches of a venting apparatus foruse in a plastic lined pipeline. The venting apparatus is fitted in thepipeline wall and comprises a through-hole to allow gas to be vented outof the pipeline, and a porous element. The porous element acts as abarrier to prevent the liner deforming under pressure and clogging thethrough-hole.

Whilst this apparatus prevents the annulus from becoming pressurised andtherefore allows plastic lined pipelines to be used for hydrocarbons, itis appreciated in the present invention that it would be a distinctadvantage to provide a vent device which allows gas to flow back intothe flowline, as opposed to a vent device which vents gas to thesurroundings. It is appreciated that in a number of circumstances it maybe undesirable for the gas contents of the fluid to be vented to theoutside of the pipeline, both from a safety and a commercialperspective. In addition, by preventing emissions from the pipeline, andretaining gas therein, the micro-annulus between the pipeline and linerwill not be exposed to the external environment and potentiallycorrosive materials and as a consequence corrosion of the pipeline willbe controlled. Similarly the liner is not exposed to any externalambient pressure which may also lead to collapse.

It is therefore an object of the present invention to provide a ventingapparatus, which prevents the annulus between a pipeline and plasticliner from becoming pressurised. In particular it is an object of thepresent invention to provide a venting apparatus which does not rely onemitting gas from the pipeline and therefore protects the annulusbetween the pipeline and plastic liner from excessive exposure tocorrosive material.

According to the present invention there is provided a pipeline assemblycomprising a pipeline, a corrosion resistant liner, and a micro-annuluslocated between said pipeline and liner, wherein the pipeline assemblyalso comprises a venting means extending through the corrosion resistantliner, wherein the venting means allows gas to flow from themicro-annulus into the centre of the pipeline assembly.

Preferably the liner is made from plastic.

In a preferred embodiment the venting means is inserted through anaperture in the plastic liner. However, in an alternative embodiment theventing means is retained by a shoulder in the wall of the plasticliner.

Preferably the venting means is a pre-fabricated assembly.

The venting means may be retained in the plastic liner by threading,gluing or fusing.

Optionally the venting means has check means for regulating fluid flow.

Said check means may be, for example, a sintered metal, a sintered wiremesh, a ceramic material or a stainless steel wire mesh. The check meanscan also be made from various plastics and composite materials such asPEEK (Poly Ether Ether Ketone) alloyed with Teflon (PAT).

Optionally, the venting means includes non-return valve means.

The non-return valve means may comprise a spring biased ball valveassembly.

Optionally the valve assembly comprises a moveable member which ismoveable between a first and second position, wherein the moveablemember is in the first position when the pressure within the pipelineexceeds a set level, and wherein the moveable member is in the secondposition when the pressure within the pipeline falls below said setlevel.

In the first position the moveable member prevents the pipeline contentsfrom exiting the pipeline.

In the second position the moveable member permits the flow of gas intothe pipeline.

Optionally the venting means may comprise a reed value arrangementformed directly in the liner.

In an alternative embodiment a sleeve member extends circumferentiallyaround the liner and longitudinally on either side of the venting meansso as to define a lengthened venting path between the micro annulus andthe centre of the pipeline assembly.

Embodiments of the present invention will now be described by way ofexample with reference to the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a first embodiment of a pipelineassembly in accordance with the present invention,

FIG. 2 is a cross-sectional end view of an alternative embodiment ofpipeline assembly,

FIG. 3 is a cross-sectional view of an alternative embodiment of apipeline assembly in accordance with the present invention,

FIG. 4 is a cross-sectional view of a further alternative embodiment ofa pipeline assembly in accordance with the present invention, and

FIGS. 5 and 6 are cross-sectional views of two designs of a furtheralternative embodiment of a pipeline assembly in accordance With thepresent invention.

Referring firstly to FIG. 1 of the drawings a pipeline assembly is showngenerally at 1. The pipeline assembly 1, is comprised of a pipeline 2,which is lined by a corrosion resistant liner 3, and an annular gap ormicro-annulus 4 defined in between the liner 3 and pipeline 2. Thecorrosion resistant liner is typically made from a plastics material. Aventing means 5 is inserted into a pre-drilled hole in the wall of theplastic liner 3. In an alternative arrangement where a relatively thickplastic liner 3 is used, the venting means 5 may be adapted to sit on‘shoulders’ within the plastic wall 3 thickness. The pipeline 2 istypically manufactured from carbon steel and transports hydrocarbons,which flow through the inside of the pipeline 10.

The venting means 5 is a pre-fabricated unit which can be inserted intothe liner 3 at any time before said liner is fitted into the pipeline 2.Typically the prefabricated venting means 5 is inserted into thepredrilled hole of the liner 3 by threading, gluing or fusing. It willbe appreciated that the through hole of the venting means 5 has specificdesign requirements such as diameter, depth and shape to provide themost effective control of corrosion.

As a consequence, the venting means 5 will typically be precisionengineered prior to insertion into the liner 3. This prefabricationprocess allows the through hole 6 of the venting means 5 to be of a moresophisticated design. A further advantage of using a prefabricatedventing means is that more thermally and chemically inert materials,such as PEEK or corrosion resistant metals can be used, to ensureperformance to specification throughout life.

The venting means 5 acts to preserve the geometric properties of thepre-drilled hole in the liner 3, that is to say, it acts essentially asa hole opener. It will be appreciated that as plastics have typicallyhigh coefficients of thermal expansion, large expansion forces occur inthe lining 3 as the pipeline 2 warms up. These forces would tend toclose any unsupported hole. Similarly, some plastics tend to swell asthey absorb water and degrade from exposure to raw hydrocarbon fluids,causing similar hole closure. Thus, the important function of theventing means 5 is to maintain the hole in the liner in an openconfiguration.

The number of venting means 5 required on the pipeline assembly 1 willvary according to, for example, the length and type of pipeline 2 used.For example the number of vents could range from one vent every 30 to 40meters of pipeline (that is one vent every few-joints) to one vent everyfew meters (that is many vents in one joint).

In use the through-hole is engineered to slow the velocity of fluid andminimise “eddies” and vortices at the steel surface, in order to slowthe replenishment of the corrosive medium. The through-hole is alsodesigned to prevent any corrosion product from being washed away, thuseffectively forming a protective layer to the substrate steel.

The example embodiment of the vent assembly shown in FIG. 1 comprises amain body, with a through hole 6 through which gas molecules can pass.The venting means 5 also comprises a non-return valve 7 having a ball 8which minimises the amount of product entering the micro-annulus. Thevalve assembly may also comprise a check means 9 for regulating fluidthrough the through-hole 6. The check means 9 has a closely controlledporosity and permeability and hence allows the fluid exchange processover the vent assembly to be closely controlled.

In use, the pipeline 2 will be subject to high pressure and temperature,under which conditions the plastic liner will have some permeability tothe gas within the hydrocarbon product contained in the pipeline 2. As aresult a small quantity of gas can enter the micro-annulus, by virtue ofthe permeability of the plastic liner 3. The venting means 5 maintainsthe pre-drilled hole in the liner 3 in an open configuration andtherefore allows gas to re-enter the pipeline from the micro-annulus.

The vent assembly embodiment shown in FIGS. 2 and 3, is also located ina pre-drilled hole of a plastic liner in a pipeline and comprises amoveable member 11, typically in the form of a disc, which during normaloperation, is pushed against the vent body 12 by the oil pressure withinthe pipeline. This prevents the product from leaving the inside of thepipeline 10 and entering the micro-annulus 6. However, in the event thatthe pressure inside the pipeline 10 falls, and there is a correspondingincrease in pressure in the micro-annulus 6, a pressure difference willarise across the liner 3, and the gas pressure will push the disc 11 offthe vent body 12 and allow gas to flow back into the centre of thepipeline 10. The end of the vent, shown in FIG. 3, is shaped to “catch”the disc 11 when the gas pressure increases and accordingly will preventthe disc 11 from being lost within the contents of the pipeline 10.

It will be appreciated that whilst the embodiments shown in FIGS. 1 to 3employ non-return valves and moveable members, the vent assembly maycomprise a much simpler design.

FIGS. 4 and 5 illustrate such a design, being similar to that shown inFIG. 1 but having no moving parts. The vent assembly shown in FIGS. 4and 5 simply acts to prevent the hole in the liner 3 from becomingclosed under the effects of the pressure and heat of the pipelinecontents 10. The hole in the liner 3 is sufficiently small to allowpressure to be relieved through it, however there is no free circulationof corrosive medium behind the liner 3.

The embodiment shown in FIG. 6 is of a similar simple design, but has acheck means 9 for regulating fluid flow through the through hole, asdescribed in FIG. 1. Various materials are envisaged for the check means9, for example sintered metal, sintered wire mesh or porcelain/ceramictype material. Additionally the check means 9 can be made from variousplastics and composite materials such as PEEK (Poly Ether Ether Ketone)alloyed with Teflon (PAT). The check means 9 acts as a baffle betweenthe surface requiring protection, that is the carbon steel pipeline 2,and the corrosive product, which typically is the hydrocarbon inside thepipeline 10 and has a closely controlled porosity and permeability whichallows the fluid exchange process to be closely controlled.

In a yet further embodiment, and in order to increase the tortuousity ofthe path between the access point of the corrosive medium and thesurface of the steel, it may be desirable to have a number of linersarranged concentrically, each with vent assemblies sufficiently offsetto allow the rapid equalisation of pressure but to effectively eliminatefree transfer of the corrosive medium between the steel and pipelinecontents.

In a still further embodiment an additional plastic sleeve may beprovided over the section of plastic pipe containing the vent, so thatany product that did travel through the vent would have an additionaldistance to travel before coming into contact with the steel pipe wall,thus reducing the likelihood of corrosion on the inside of the steelpipe as turbulent fluid straight from the pipe would never be inimmediate contact with the steel.

The sleeve would be added after the liner had been swaged to fit thehost pipe, but before the liner itself was inserted into the pipe. It isenvisaged that the sleeve would be applied by wrapping it around theliner pipe.

The advantage of the present invention lies in the fact that the ventassembly acts to allow gas to flow from the micro-annulus between thepipeline and liner, back into the contents of the pipeline as opposed toventing the gas to the surroundings. As a result there are no emissionsfrom the pipeline. This has both commercial and environmental advantagesand pollution of the environment surrounding the pipeline will begreatly reduced.

Although various arrangements of vent assembly have already beendiscussed it is not envisaged that the examples discussed should belimiting and other possible arrangements will be readily apparent to theskilled engineer. One such arrangement envisaged is that of having thevent shaped as a reed valve. The “vent” would be made by using a chiselto gouge into the liner, creating a sliver of liner which would remainclosed until subjected to a pressure difference, which would allow therelease of the pressure trapped in the annular gap. The reed valve wouldbe formed on the inside of the plastic liner, at some point prior to itsinsertion into the steel host pipe.

Modifications and improvements may be made without departing from thescope of the invention herein intended.

1. A pipeline assembly for the transportation of fluid, the pipelineassembly comprising a pipeline, a corrosion resistance plastic liner,and a micro-annulus located between said pipeline and liner, wherein thepipeline assembly also comprises a venting means extending through thecorrosion resistance plastic liner, wherein, during transportation offluid in the center of the pipeline assembly, the venting means allowsgas to flow from the micro-annulus into the centre of the pipelineassembly by a flow path wholly internal of the pipeline.
 2. A pipelineassembly as claimed in claim 1 wherein the venting means is insertedthrough an aperture in the plastic liner.
 3. A pipeline assembly asclaimed in claim 2 wherein the venting means is retained by a shoulderin the wall of the plastic liner.
 4. A pipeline assembly as claimed inany one of the preceding claims wherein the venting means is aprefabricated assembly.
 5. A pipeline assembly as claimed in claim 1wherein the venting means is retained in the plastic liner by threading,gluing or fusing.
 6. A pipeline assembly as claimed in claim 1 whereinthe venting means has check means for regulating fluid flow.
 7. Apipeline assembly as claimed in claim 6 wherein said check means is of aconstruction selected from a group comprising a sintered metal, asintered wire mesh, a ceramic material, a stainless steel wire mesh, aplastics material and composite materials such as PEEK (Poly Ether EtherKetone) alloyed with Teflon®.
 8. A pipeline assembly as claimed in claim1 wherein the venting means includes non-return valve means.
 9. Apipeline assembly as claimed in claim 8 wherein the non-return valvemeans comprises a spring biased ball valve assembly.
 10. A pipelineassembly as claimed in claim 8 wherein the valve means comprises amoveable member which is moveable between a first and second position,wherein the moveable member is in the first position when the pressurewithin the pipeline exceeds a set level, and wherein the moveable memberis in the second position when the pressure within the pipeline fallsbelow said set level, wherein in the first position the moveable memberprevents the pipeline contents from exiting the pipeline and wherein inthe second position the moveable member permits the flow of gas into thepipeline.
 11. A pipeline assembly as claimed in claim 1 wherein theventing means comprises a reed valve arrangement formed directly in theliner.
 12. A pipeline assembly as claimed in claim 1 wherein a sleevemember extends circumferentially around the liner and longitudinally oneither side of the venting means so as to define a lengthened ventingpath between the micro annulus and the centre of the pipeline assembly.13. A pipeline assembly as claimed in claim 1 wherein the fluid is ahydrocarbon.
 14. A pipeline assembly as claimed in claim 13 wherein thehydrocarbon comprises a liquid phase and a gas phase.
 15. A pipelineassembly as claimed in claim 14 wherein the venting means is adapted fortransporting the gas phase by the flow path.
 16. A method of forming apipeline assembly from a pipeline and a corrosion resistant plasticliner, the method comprising the sequential steps of: providing athrough hole in the corrosion resistant plastic liner; inserting apre-fabricated venting means into the through hole in the corrosionresistant plastic liner; and inserting the corrosion resistant plasticliner into a pipeline such that, during transportation of fluid in thecenter of the pipeline assembly, the venting means allows gas to flowfrom a micro-annulus located between said pipeline and corrosionresistant liner into the centre of the pipeline assembly.
 17. The methodas claimed in claim 16, comprising the additional step of threading theventing means in a pre-drilled hole.
 18. The method as claimed in claim16, comprising the additional step of gluing the venting means in apre-drilled hole.
 19. The method as claimed in claim 16, comprising theadditional step of fusing the venting means in a pre-drilled hole.
 20. Apipeline assembly formed by the method of claim 16.